1. Field of the Invention
The present invention generally relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a semiconductor device having a gate electrode of a short gate length.
2. Description of the Related Art
MESFETs (Metal Semiconductor Field Effect Transistors) and HEMTs (High Electron Mobility Circuits) are used in MMICs (Microwave Monolithic Integrated Circuits) handling high frequencies and high output powers. MESFETs and HEMTs are Schottky type field effect transistors using compound semiconductors such as GaAs. It is important to reduce the gate length in order to improve high-frequency characteristic of MESFETs and HEMTs.
There are several methods to form the gate electrodes of short gate lengths. For example, Japanese Patent Application Publication No. 10-125698 discloses a method to realize a gate electrode of a short gate length. According to this publication, a dummy gate formed on a semiconductor substrate is narrowed by dry etching with oxygen plasma, and an SiO2 film is subsequently formed on the semiconductor substrate. Then, the dummy gate is removed, and a gate electrode is formed in an area from which the dummy gate has been removed.